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EVISED AND ENLARGED EDITION. 

■■--SHORT METliOtJS*- 

G 1628 

G62 — F0R — 

IH\ COMPUTING 

NTEREST and DISCOUNT. 



100 DAYS INTEREST RULE. 



HENRY GOLDMANJK 

nthor of the ' l Electric Detector, " " New System for 

Detecting Errors in Trial Balances" " ioo Days 

Average Rule" etc. 



New York, 

' ho £7 fr 

1884. 



Copyright, 1884, by HENRY GOLDMANN. 



All Rig his Reserved. 



Is the money paid for the use of money ; Prin 
ci pal, the money on which interest is paid 
Rate of Interest, the number of per cent., an< 
Amount, the principal plus the interest. 

To find the interest if the time is givei 
in days. 

100 DAYS INTEREST RULE. 

i. Divide the principal by one of the ke; 
numbers of the following table *: 

The units of the cents of the principal can be omitted 
their interest being, as a rule, too small to be considered 

2. Add to or subtract from the result th< 
part which the corresponding column indicates. 

The part has to be taken of the result of the divi 
sion by the key number. Where no part is indicated 
the division by the key number is sufficient. 

The result is the interest of the given princi 
pal, at the given rate, for i, 10 or ioo days, ac 
cording to how many places to the left the deci 
mal point is removed; i place for ico days, i 
places for 10 days and 3 places for 1 day. 

To obtain the interest for any given numbe 
of days, multiply the hundreds, tens or units o 
days by the corresponding amount of interest 
and add the products together. 

Note. — If the given number of days is between 90 and 100, it i 
more practical to deduct from the interest for 100 days as many time 
the interest for 1 day as there are days less. 

* The key numbers for the most frequent rates can b 
easily remembered, being the result of 36 divided b 
tl^e given rate. 



,10/ 

PROFIT AND LOSS. 



Some important questions, frequently oc- 
curring in business, find their practical solution 
in the following lines : 



To ascertain the rate of the profit or 
loss, if the cost price is taken as base. 



Multiply the difference between the cost and 
the selling price by ioo y and divide the product 
by the given cost price. 



To ascertain the rate of the profit or 
loss, if the selling price is taken as base. 



Multiply the difference between the cost and 
the selling price by ioo, and divide the product 
by the given selling price. 



Note. —If the selling price is larger than the cost price, the answer 
is a profit. If the cost price is larger than the selling price, the an- 
swer is a loss. 



The profit on the cost price can reach any 
number of per cent , while the profit of the sell- 
ing price can only reach ico %-, as in this case 
the cost price is reduced to o. 



fty6*5 



^ INTEREST -H-hf, 

•G 

Is the money paid for the use of money ; Prin 
cipal, the money on which interest is paid 
Rate of Interest, the fiumber of per cent., an< 
Amount, the principal plus the interest. 

To find the interest if the time is givet 
in days. 

100 DAYS INTEREST RULE. 

i. Divide the principal by one of the ke; 
numbers of the following table *: 

The units of the cents of the principal can be omitted 
their interest being, as a rule, too small to be considered 

2. Add to or subtract from the result th< 
part which the corresponding column indicates; 

The part has to be taken of the result of the divi 
sion by the key number. Where no part is indicated 
the division by the key number is sufficient. 

The result is the interest of the given princi 
pal, at the given rate, for i, 10 or ioo days, ac 
cording to how many places to the left the deci 
mal point is removed; i place for ico days, 
places for 10 days and 3 places for 1 day. 

To obtain the interest for any given numbe 
of days, multiply the hundreds, tens or units o 
days by the corresponding amount of interest 
and add the products together. 

Note. — If the given number of days is between 90 and 100, it : 
more practical to deduct from the interest for 100 days as many time 
the interest for 1 day as there are days less. 

* The key numbers for the most frequent rates can b 
easily remembered, being the result of 36 divided b 
tUe given rate. 



■* INTEREST**; 



Is the monej' paid for the use of money ; Prin- 
cipal, the money on which interest is paid ; 
Rate of Interest, the cumber of per cent., and 
Amount, the principal plus the interest. 

To find the interest if the time is given 
in days. 

100 DAYS INTEREST RULE. 



2. Add to or subtract from the result the 
part which the corresponding column indicates.- 
ken of the result of the divi- 



donbyth 



Whe 



The result is the interest of the given princi- 
pal, at the given rate, for i, 10 or ioo days, ac- 
cording to how many places to the left the deci- 
mal point is removed ; i place for ico days, 2 
places for 10 days and 3 places for 1 day. 

To obtain the interest for any given number 
of days, multiply the hundreds, tens or units of 
days by the corresponding amount of interest, 
and add the products together. 



* The key numbers for the 
easfly remembered, being the 



RATE 


Key Number 


PART 


Per cent. 


Divldeby 


to be added. 


to be deducted. 


I'A 


12 


On 


-sixth. 






VA 

5 

sA 


8 






On 
One 


"■sixth. 


6/ 2 

7 

7A 

8 

9 

18 


6 
6 

3 
3 
3 
3 


One 
On 

One 
On 

One- 


twelfth, 
■sixth. 

|.,.iru-r. 

quarter. 


On 
One 


e-sixth. 
twelfth. 



EXAMPLES. 




1. $763.— .at 6 % for 


93 days. 


6)763-00 
1271 =Interestfor 100 days. 

7X0-127= 89 = " " 7 " 

Answer: $11 82 =Interest for 93 days. 


2. $136.43 at s %" for 


113 days. 


6)136-43 




—6 '37 
1X1-90= i- 9 o=Interes 
1X0-19= 19= " 

3X0-02= 6= « 

Answer: $2-15 =Interest 


" 3_ " 

for 113 days. 



SHORT INTEREST RULE. 

For the following rates and the corresponding 
number of days the interest is found without any 
calculation, by simply removing the decimal 
point of the principal two places to the left. 



360 days. 



EXAMPLE. 

$365.44 at 6% for 54 days. 






$3-6s 6% for 60 days. 
- -37 6% "- 6 " 

Answer: S3. 2 8 6% for 54 days. 

The "100 Days Interest Rule" permits a 
general application, while the "Short Interest 
Rule" will be found practicable in a number of 
special cases. Both rules combined give an in- 
terest method, which has no equal. 



Note. -To ascertain the intere 
at 365 days, apply the Rules st 
one-seventy.fhird (±) from the a 



t, if the 



To find the interest on several items 
without figuring the interest for each 
item separately. 

Any item showing its own interest at the rate 
of 36 % for 

10c days, by removing the decimal point 1 place to the left 
10 ','. ", .',' ,'i 2 P lf CeS ", ',', 

the interest for any given number of days car, 
be easily obtained by multiplying the interest for 
1, 10 or 100 days of each item by the units, 
tens or hundreds of the corresponding number 
of days. 

These products added together, give the inter- 
est on all items at 36%. 

To obtain the interest for any other given rate, 
divide the sum of the products by one of the key 
numbers of the preceding Table, according to 
the rate, and add or deduct the part which the 
corresponding column indicates. 

Example : 

Find the interest on the following items at the 
rate of 6%. 

$360.00 for 16 days j^° 

7218 " 29 " Vt 

129.36 "34 " J 3-^8 

87.40 "80 " 6.99 

(4.03 

40.29 "112 " -; 40 

6)23.75 

Answer : $3.95 



To find the interest if the time is given 
in months: 

Multiply the number of months by 30, which 
gives the corresponding number of days, and 
apply the "100 Days" or the "Short Interest 
Rule." 

EXAMPLE. 
$125.— .at 7% for 3 months and 12 days. 
6)125.00, 3X3°+i2=io2 days. 

208 Interest for 100 days=$2.43 

+ 6 35 " " _J_ " = 5 

2.43, Interest for io2daye=$2.48 

To find the interest if the time is given 

in years : 

Multiply the principal by the product of the 

number of years and the rate, and remove the 

decimal point two places to the left. 

To find the interest for one rear, multiply the 
principal by the rate, and remove the decimal 
point two places to the left. 
To find the principal: 

1. If the time is given in days, multiply the 
interest by 36, divide by the product of the num- 
ber of days and the rate and remove the decimal 
point three places to the right. 

2. If the lime is given in months, multiply the 
interest by 12, divide by the product of the num- 
ber of months and the rate and remove the deci- 
mal point two places to the right. 

3. If the lime is given in rears, divide the inter- 
est by the product of the number of years and 
the rate and remove the decimal point two places 
to the right. 



To find the rate : 

Apply the rules given fur finding the principal, 
substituting the principal for the rate. 

To find the time : 



by the pre 



vide by tin 
right! 6 " 101 



itf, multiply the interest by 36, divid 
.tct of the principal and the rate, an 
decimal point three places to th 

mlhs, multiply the interest by 12, di 
product of the principal and the rati 
■ the decimal point two places to th 



of the principal and the rate, and remove the 
decimal point two places to the right. 

PRESENT WORTH. 

To ascertain the principal which, at a 
given rate and in a given time, produces 
a given amount. 



by the 
36, « 



If ft 



ant by tl. 
// the , 



by the numbei 
the left) add 1 



, multiply the 



: two places to 
tnd divide the 



To ascertain the amount which, after 
deducting the interest at a given rate 
and for a given time, leaves a given 
principal. 

Apply the rules stated for finding the princi- 
pal, with the deviation that instead of adding 
i unit to the quotient deduct the quotient from 
i unit, and substitute the given principal for the 

ACCOUNT CURRENTS. 

An Account Current is a copy of the debit 
and credit entries of an account, with interest 
charged or credited thereon. 

Account Currents are given by business or 
banking houses to their customers or corres- 
pondents, either quarterly, semi-annually or 
annually. 

EULES POE CLOSING! AN ACCOUNT OUEEENT, 

of the month or the earhc.-t ibtc and the il.itc- .7r c.u h 

it items (page 5). 

3. rigure also the interest on the balance of the account 
or the number of days between the beginning of the 

5 closed, and place the same under the inters! items of 

1 -ide of the account. 

4. Add then the interest items of the debit and credit 

omputed therefrom :U the given ..vie (Unlc, nageslon 
he same side of the account. • V h i) 

5 I he 36",; ml re t hems arc n » in balance rnd the 



36",,. at 



COMPOUND INTEREST 

Is the interest on the sum of a given principal 
and the interest (added in certain intervals of time, 
mostly annually or semi-annually). 

See " Rules for Calculating Rapidly," page II. 

•^DISCOUNT*- 



is an allowance for the payment of money before 
it becomes due. 

The difference between interest and discount 
is mainly this, that the former is added to a given 
principal, while the latter is deducted from a 

Discount is figured at a certain rate, either 
without any given time, in which case one year 
is taken as the base, or for a given number of 
days. The rules for computing interest find ap- 
plication in both cases. 

LIST DISCOUNT 

Is a deduction from the list price or the amount 
of a bill, customary in many branches of business. 
If only a single rale should be deducted, the net 
price or net amount is easily obtained by sim- 
ply subtracting the rate from 100, multiplying 



: from 1 
the list price or the given amount by the differ" 
ence, and removing the decimal point of the 
product two places to the left. 



EXAMPLE. 
.2.00; list discount, 15%. 



Answer, $35.70 Net price. 

If several rates should be deducted successively, 
subtract each of the given rates from 100, mul- 
tiply the differences, and place the decimal point 
in front of the product. The list price or the 
amount of bill multiplied by this product gives 
the desired net price or net amount. 



EXAMPLE. 



st prices, $425.0' 



60* X 80* X 9S = 456,ooo* 



•45 6 
193.800 






PROFIT AND LOSS. 



Some important questions, frequently 
iurring in business, find their practical solut 
n the following lines : 



e of the profit er 



Multiply the difference between the cost and 
the selling price by 100, and divide the product 
by the given cost price. 



Multiply the difference between the cost and 
the selling price by 100, and divide the product 
by the given selling price. 



The profit on the cost price can reach any 
number of per cent , while the profit of the sell- 
ing price can only rench rco %•, as in this case 
the cost price is reduced to o. 



lllllllilllllllfl 
To g a4n „n me {{] Qffl 331 581 

5 %, divide the same oy 20, am multiply the result by 



r/«;» of the 

",„ divide the cos 



and multiply the result hy 



— II- 



tf* ROFiT AN LO 






Some important questions, frequently oc- 
curring in business, find their practical solution 
in the following lines : 



To ascertain the rate of the profit or 
loss, if the cost price is taken as base. 



Multiply the difference between the cost and 
the selling price by ioo y and divide the product 
by the given cost price. 



To ascertain the rate of the profit or 
loss, if the selling price is taken as base. 



Multiply the difference between the cost and 
the selling price by ioo, and divide the product 
by the given selling price. 



Note. —If the selling price is larger than the cost price, the answer 
is a profit. If the cost price is larger than the selling price, the an- 
swer is a loss. 



The profit on the cost price can reach any 
number of per cent , while the profit of the sell- 
ing price can only reach ico % % as in this case 
the cobt price is reduced to o. 



LIBRARY OF CONGRESS 



To gain on the < Q Q27 331 581 



r 0/ 

5 /"> 


divide the 


same oy2o, \ 


10 ' 


it t 


ic, 


i5 " 


(2 
tt 


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20, 


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21 
II 

9 
2 3 
12 

^/ 
T 3 

4 
27 
14 
29 
15 
16 

5 
17 

18 

19 



To r/r/m of the selliiu/ price : 



^ divide the cost price by 1 9 and multiply the result by 20 



10 



I2J£ 


u a 


15 


<< u 


20 


a (( 


25 


u a 


3° 


a t« 


33M 


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LIBRARY OF CONGRESS 



027 331 581 



